The present invention concerns a device in a time piece for feeding an electro-luminescent display with impulses.
A means for replacing the mechanical display in a time piece consists in using electro-luminescent diodes (called "LED") for forming the display symbols, the current consumption of which is relatively low. This is an advantage in watches operated from batteries. It is known that these LED diodes have a luminous yield which increases with the current traversing the diodes. On this account FIGS. 1 and 2 show for two types of diode, the relative yield .eta. as a function of the current.
For a watch battery, a current of 100 mA represents a high consumption: however, for a watch display, it is not necessary to feed the current continually to the LED which is to be lit up: it can be impulse-operated provided that the illumination frequency does not fall below 30Hz. Above that frequency, a human eye sees the light emitted as constant. A system for supplying LED diodes by impulses is known in which the current is induced in a coil by a commutator. However, present-day batteries have internal resistances which are relatively high and cannot readily provide the peak currents necessary.